Mechanic of Mechanic of breathingbreathing

By prof. Dr.By prof. Dr.

Soheir helmySoheir helmy

Definition Definition

Transport of oxygen from Transport of oxygen from atmosphere to tissue atmosphere to tissue

Oxidation of food stuff and Oxidation of food stuff and removal of CO2removal of CO2

Classification:Classification:

1- External respiration1- External respiration Pulmonary ventilationPulmonary ventilation

Gas exchange Gas exchange

2- Carriage of gases (O2, CO2) 2- Carriage of gases (O2, CO2) by blood.by blood.

3- Internal respiration. 3- Internal respiration. ,I ,I

Respiratory cycle:Respiratory cycle:Each respiratory cycle consists ofEach respiratory cycle consists of

- 1-Inspiration:- 1-Inspiration: Active process (needs energy)Active process (needs energy) Contraction of respiratory muscles (diaphragm and Contraction of respiratory muscles (diaphragm and

intercostal muscles)intercostal muscles) Thoracic cavity increase and air rush in.Thoracic cavity increase and air rush in. Its duration 1.3Its duration 1.3 sec.sec.

Respiratory cycle:Respiratory cycle:

2-Expiration:2-Expiration: Passive processPassive process Relaxation of respiratory muscles Relaxation of respiratory muscles Reduction of the thoracic cavity size Reduction of the thoracic cavity size Air rush out Air rush out Duration 1.7 secDuration 1.7 sec. .

3-Expiratory pause.3-Expiratory pause.

Mechanics of respirationMechanics of respiration

Muscles of respirationMuscles of respiration

1-diaphragm:-1-diaphragm:- It is responsible for It is responsible for

about 75% of about 75% of respirationrespiration

Contraction of Contraction of diaphragm leads to diaphragm leads to its descend from 1.5-its descend from 1.5-7cm7cm

It is supplied by It is supplied by phrenic phrenic nerve(cervical 3,4,5)nerve(cervical 3,4,5)

Muscles of respirationMuscles of respiration

2-External intercostal Ms.:2-External intercostal Ms.: Their Contraction increase the Their Contraction increase the

antero-posteriorantero-posterior diameter and diameter and transverse diameter of the chest.transverse diameter of the chest.

Nerve supply:1-10 thoracic Nerve supply:1-10 thoracic segmentssegments..

Mechanics of Inspiration:Mechanics of Inspiration:

As a result of contraction of both As a result of contraction of both DiaphragmDiaphragm and Intercostal msand Intercostal ms.:.:

Chest increase in all its dimensions.Chest increase in all its dimensions. Lung follows the chestLung follows the chest passively.passively. Lung volume increase and the intra Lung volume increase and the intra

pulmonary pressure decrease to about -2 pulmonary pressure decrease to about -2 mmHg.mmHg.

Intra pleural pressure decrease to -6 Intra pleural pressure decrease to -6 mmHgmmHg

Air rush in (inspiration).Air rush in (inspiration).

How Expiration occurs How Expiration occurs

Relaxation of respiratory Ms.Relaxation of respiratory Ms. Chest decrease in all its dimensions.Chest decrease in all its dimensions. Lung volume decrease & intra Lung volume decrease & intra

pulmonary pressure increase to pulmonary pressure increase to about +2 mmHg.about +2 mmHg.

Air rush out (expiration).Air rush out (expiration).

Forced respiration:Forced respiration:

Forced inspiration:Forced inspiration:

Accessory muscles of respiration Accessory muscles of respiration (sternocleiomastoid, serratus (sternocleiomastoid, serratus anterior & scalini muscle)anterior & scalini muscle)

Forced expiration:Forced expiration:

Active process contraction of Active process contraction of abdominal muscles & internal abdominal muscles & internal intercostal. intercostal.

Pulmonary ventilationPulmonary ventilation

Air flow to the lungAir flow to the lung It is affected by :It is affected by : 1- Resistance of the air passage.1- Resistance of the air passage. 2-pressures in the thoracic 2-pressures in the thoracic

cavity( I.P.P & I.Pul.P)cavity( I.P.P & I.Pul.P) 3- surfactant3- surfactant 4-lung & chest compliance.4-lung & chest compliance.

Factors affecting pulmonary ventilation

Resistance of respiratory passage

Pressure relationship in

thoracic cavity Surfactant

Chest and lung compliance

Bronchial muscle tone

Bronchial mucosa

Pressure gradient

Diameter of air passege

Expiration bronchoconstriction

InspirationBronchodilatation Chemical Nervous

Reflex A.N.S.

Bronchial muscle toneBronchial muscle tone

Nervous factors:-Nervous factors:- Autonomic nervous systemAutonomic nervous system Sympathetic >>>>>bronchodilation.Sympathetic >>>>>bronchodilation. Parasympathetic>>>>bronchoconstriParasympathetic>>>>bronchoconstri

ction.ction. Chemical factors:-Chemical factors:- Histamine>>>constrictionHistamine>>>constriction Serotonin>>>constrictionSerotonin>>>constriction Platelet activating factorPlatelet activating factor

Intra pulmonary Intra pulmonary pressurepressure

It is the pressure inside lung alveoli. It is the pressure inside lung alveoli. It is connected to the atmosphere.It is connected to the atmosphere.

It equals -2mmHg during inspiration.It equals -2mmHg during inspiration. +2mmHg during expiration.+2mmHg during expiration. It equals atmospheric pressure in It equals atmospheric pressure in

the expiratory pause.the expiratory pause.

Intra pleural pressureIntra pleural pressure

It is the pressure inside the pleural It is the pressure inside the pleural cavity.cavity.

It is a negative pressure.It is a negative pressure. It equals -3mmHg during expiration.It equals -3mmHg during expiration. It equals -6 mmHg during It equals -6 mmHg during

inspiration.inspiration.

surfactantsurfactant

It is a lipoprotein substance.It is a lipoprotein substance. It is synthesized and released from It is synthesized and released from

type 11type 11 alveolar cells.alveolar cells. Functions of surfactant:-Functions of surfactant:- 1-it decreases the surface tension of 1-it decreases the surface tension of

the fluid lining the alveoli so it helps the fluid lining the alveoli so it helps lung expansion.lung expansion.

It may activate and exert stimulant It may activate and exert stimulant effect on macrophage.effect on macrophage.

surfactantsurfactant

It has a bacteriolytic effect, It has a bacteriolytic effect, rendering the bacteria more rendering the bacteria more susceptible to alveolar macrophage.susceptible to alveolar macrophage.

It assists the ciliary movement of It assists the ciliary movement of upper respiratory tract.upper respiratory tract.

Surfactant decrease in :-Surfactant decrease in :- Respiratory distress syndrome. Respiratory distress syndrome. cigarette smoking.cigarette smoking.

compliancecompliance

Ability of the lung and chest to expand.Ability of the lung and chest to expand. Expansibility of the lung and chest wall.Expansibility of the lung and chest wall. Factors affecting:-Factors affecting:- Lung factorsLung factors Elastic force of the lung tissues, Elastic force of the lung tissues,

compliacce decreases in cases of fibrosis.compliacce decreases in cases of fibrosis. Surface tension of the lung and surfactantSurface tension of the lung and surfactant

compliancecompliance

Factors in the chest wallFactors in the chest wall The elastic properties of the thorax The elastic properties of the thorax

are caused by the natural elasticity are caused by the natural elasticity of muscles, tendons and connective of muscles, tendons and connective tissues of the chest.tissues of the chest.